Built to blast: See how researchers turn diamonds into super sensors

Diamond-based electronics can handle the toughest environments, from the deep sea to outer space. Learn how UAB researchers are creating unique sensors in the Diamond Microfabrication Laboratory.

Everyone knows that diamonds are tough. They’re also highly resistant to corrosion and radiation, which means they are perfect for duty in all kinds of rough environments, from the deep sea to outer space. That’s why researchers in UAB’s Center for Nanoscale Materials and Biointegration (CNMB) are so excited about the potential for their unique diamond-based sensors, which encase metallic circuits under a protective layer of synthetic diamond (see below).

While silicon circuits are limited to temperatures below 100 degrees Celsius, diamond circuits can function at temperatures up to 600 degrees Celsius. “You can put them in a jet engine exhaust and they still work well,” said Yogesh Vohra, Ph.D., CNMB director, University Scholar and professor in the UAB College of Arts and SciencesDepartment of Physics.

The sensors could be used in oil and natural gas drilling operations, to register conditions on the sea floor, Vohra says, or to monitor equipment in the frigid environment of outer space. Another application: keeping an eye on conditions inside coal-fired power plants. Currently, plants have to shut down for days in the event of a leak in their exhaust towers so that the structures can cool enough for human inspectors to enter. But a diamond-based sensor could do the job immediately. “There is lots of untapped potential,” he said.

The initial market for the center’s diamonds, when it enters full production mode next year, is in research devices known as designer diamond anvils. These devices are used to measure the properties of materials under extreme conditions of pressures and temperatures. “There is a unique product-market fit for our technology in sensors for extreme environments,” said Vohra (above, right, with graduate student Samuel Moore).

In the UAB Diamond Microfabrication Lab, researchers use two patented processes to turn small gemstones into sensors capable of handling the most extreme environments on earth — and beyond.

Here’s how they do it:

Step 1: Diamond, Meet Tungsten

The process begins with a one-third-carat single crystal gem diamond.

Here, Gopi Samudrala, Ph.D., a research associate in the CNMB, loads several diamonds into the Microfab Lab’s sputter machine, which coats them in a layer of tungsten.

Step 2: Draw the Pattern

The real magic happens in the lab’s Class 7000 clean room, where the tungsten-layered diamond is further spin-coated with a polymer photo-resist and then exposed to light radiation that etches the desired circuit pattern onto the polymer. The room’s strong red lighting is specially calibrated so that it will not interfere with this process.

Researchers first draw their circuit on a computer, then transfer the design to the adjacent lithography machine, which uses light to etch a pattern in the tungsten.

Step 3: Etch the Circuits

The researchers have developed a special technique — 3D “mask-less” photolithography — which “gives us the freedom to draw anything on the diamond,” without the expensive masks that are normally used for the process, Vohra explained. His team is the first to ever apply 3D mask-less lithography to diamonds. “In terms of microcircuit design on diamond, we really are limited only by our imaginations,” Vohra said.

The technique is extremely precise; each sensor is five microns wide, less than one-tenth the size of a human hair. The researchers demonstrate this precision by etching a perfect re-creation of UAB’s logo (see inset). The lithography machine sits on a 1,500-pound block of granite, one of several measures taken to dampen vibrations. Another is the lab’s strategic location in its building, chosen to put it as far as possible from passing traffic outside. “When you’re working on the order of a few microns, nothing is easy,” said Samuel Moore (above, left), a graduate student whose thesis is based on this project.

“Our goal is to have multiple sensors on top of each other,” Vohra said. “Think of them as multitasking diamond-based sensors.”

Step 4: Take a Bath

The extraneous tungsten is removed in a bath of weak acid and exposed to other proprietary solutions.

Step 5: Bring on the Diamond Coating

In another lab a few blocks away, the sensors are completely encapsulated in a synthetic, single-crystalline diamond coating. The researchers create the outer diamond using a mix of methane and hydrogen in a UAB-patented process known as microwave plasma chemical vapor deposition.

Step 6: Quality Assurance

Samudrala inspects the finished product (above and below). The entire process lasts about a day and a half from start to finish.

The team now is developing a wireless version of its diamond-based sensor, something that has never been done. “But we like the challenge,” Vohra said. He predicts that, in less than two years, “we’ll have new innovations in wireless communications with diamond-based sensors.”